CSO Aesthetics and Static Screening Technologies

In most countries the principal assets for the conveyance of surface water runoff in the urban area are sewers. In older urban areas the sewer systems are mainly combined where domestic and industrial effluents are conveyed in the same pipes of the system. Combined sewer overflows (CSO's) are constructed to relieve the system of the excess flows that cannot be accommodated by the downstream sewers or the treatment works, thereby reducing the risk of surcharge and surface flooding in the catchment upstream of the CSO. A primary function of such CSO structures is to retain the pollution within in the combined sewer flow such that it is discharged to the treatment works. Such pollution comprises aesthetics (floaters), finely suspended solids and pollutants in solution. Current practice has seen the use of storage tank structures to retain these pollutant effluents in the system but it has recently been recognised that, for the retention of aesthetic solids, the inclusion of storage may not be the most cost effective option and that new screening technologies may be employed to retain and treat the pollutants in the flow prior to its discharge to the receiving watercourse. This paper describes a study that has been completed to monitor the performance of a static screen to retain aesthetic solids in a CSO chamber.